The general purpose of the research is to elucidate the mechanisms of intestinal absorption and secretion with emphasis on fluid secretion. It is proposed to extend our studies of (1) the microvascular pattern of the intestinal villus and the flow within it by the appropriate combined use of microspheres and silicon rubber injection, including the response to perturbing influences, and (2) the pathophysiology of the secretion associated with intestinal obstruction, with particular emphasis on whether bacterial enterotoxins are important initiating factors. Bibliographic references: B. Sircar, D.G. Levitt, and N. Lifson. Distributions of flow in microvasculature of rabbit small intestine studied by (a) latex injection and (b) direct microsphere localization. Abstracts of 1st International Congress for Microcirculation. Toronto, Canada, June 1975.